1. Field of the Invention
This invention relates to the development of low viscosity polyester polyols which are liquid at room temperature and can be processed on conventional machines using the polyisocyanate-addition polymerization process, to form cellular and/or noncellular plastics exhibiting excellent mechanical properties.
This invention further relates to the use of 2-methyl-1,4-butanediol in the preparation of low viscosity polyester polyols which are liquid at room temperature.
2. Description of Material Art
The preparation of polyester polyols and their use for the preparation of polyurethane plastics using the polyisocyanate-addition polymerization process is well known from numerous literature and patent publications. Specifically, reference is made to the Plastics Handbook, Vol. 7, Polyurethanes, 1st Ed., 1966, published by A. Hoechtlen and R. Vieweg, and the 2nd Ed., 1983, published by G. Oertel, Carl Hanser Publishers, Munchen, Vienna.
Polyester polyols are commonly prepared using polycarboxylic acids and multivalent alcohols by molten state condensation in the presence of acids or metal salts used as catalysts. The polycondensation is carried out under reduced pressure, and the water formed during the polycondensation is distilled out of the reaction mixture in order to drive the equilibrium of the reaction toward polyester formation. In this manner, polyester polyols can be prepared having acid numbers greater than 5, in relatively short reaction times.
Polyester polyols, especially those based on adipic acid and alkanediols, alkanediol mixtures or mixtures of alkanediols and higher valent alcohols, are used in large quantities for the preparation of polyurethane plastics for a variety of applications. However, these polyols suffer from certain disadvantages. One particular disadvantage is that the polyester polyols under usual storage conditions completely or partially crystallize and exhibit such high viscosity that they cannot be directly processed, at room temperature using the polyisocyanate-addition process, on conventional machines to form plastic materials. According to the prior art, the polyester polyols must be melted and homogenized in externally protected devices, and then reacted at elevated temperatures in costly temperature controlled devices. Thus, the preparation of polyurethane molded articles is more expensive.
In order to avoid this disadvantage, as disclosed in EP-PS No. 017 060, for the preparation of polyurethane elastomers, and as disclosed in U.S. Pat. No. 4,362,825 (EP-PS No. 056 122) for the preparation of flexible polyurethane foams, liquid polyester polyols are used which have hydroxyl numbers from 40 to 80, and are obtained through the polycondensation of organic dicarboxylic acids with polyol mixtures comprised of at least four di- and trivalent alcohols based on 1,4-butanediol, 1,6-hexanediol, 1,5 pentanediol, and/or diethylene glycol and an alkanetriol, such as glycerin and/or trimethylolpropane, in certain defined quantity ratios. The polyurethane elastomers obtained in this manner possess extremely favorable cold tolerance and excellent hydrolysis resistance. The elastomers also possess high mechanical sturdiness as well as very good compression permanent sets. The polyurethane flexible foams also demonstrate, in addition to improved hydrolysis resistance, very good punching ability. Such polyol mixtures are, however, relatively expensive, since the starting components are obtained partially through the reduction of the corresponding dicarboxylic acid mixtures and are only available in limited amounts for the preparation of polyester polyols. Moreover, the ability to conduct polycondensation reactions requires a certain technical aptitude.
U.S. Pat. No. 4,052,358 (DE-OS No. 26 09 208) describes pigmentable unsaturated polyester resin compositions having limited shrinkage. The polyester resin composition comprises a mixture of from 15 to 70 mole percent of neopentyl glycol and from 10 to 30 mole percent of 2,2, Bis-(4-hydroxylcyclohexyl)-propane as glycol components. The glycol components can include an additional multivalent alcohol of from 1 to 15 mole percent. A preferred multivalent alcohol is 2-methyl-1,4-butanediol.
The object of the present invention is to develop polyester polyols which are liquid at room temperature, have viscosities which are as low as possible, and which can be processed relatively problem-free on conventional machines using the polyisocyanate-addition polymerization process to form non-cellular or cellular plastics demonstrating good mechanical properties.
This objective can be surprisingly achieved by the complete or partial use of 2-methyl-1,4-butanediol as a multivalent alcohol in the preparation of polyester polyols.